Synthesis of phthalonitrile resins containing ether and imide linkages

ABSTRACT

Imide-containing phthalonitrile monomers are synthesized into heat resistant polymers and copolymers with aromatic ring structure incorporating imide and ether linkages. The synthesis of the high temperature thermosetting polymers and copolymers is also disclosed.

This application is a divisional application of U.S. patent Ser. No.07/352,327, now U.S. Pat. No. 5,003,078 filed May 16,1989.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates, in general, to high temperature materials and,in particular, to a new class of aromatic phthalonitrile monomerscontaining ether and imide linkages and their conversion to hightemperature thermosetting polymers and copolymers and the synthesisthereof.

2. Description of the Prior Art

Interest in fiber-reinforced composites for advanced aerospaceapplications has led to the search for high temperature polymers thatare easily processed and exhibit high thermal and oxidative stability.Presently, epoxies and polyimides are used. These materials havesuperior mechanical properties and are lighter and more economical toproduce than metals but lack the thermal stability to operate at hightemperatures and tend to oxidize and become brittle over time.Conventional epoxy-based composites and adhesives are limited to 120° C.maximum, have a problem with water absorption and require lowtemperature prepreg storage. Polyimides can produce gaseous productswhen cured, resulting in voids and blisters in composite components.

Phthalonitrile polymers constitute a recent and important class ofhigh-temperature materials, having a wide range of uses, such ascomposite matrices, adhesives, sealants, and even semiconductors. Thesepolymers are prepared from phthalonitriles in which the linking groupbetween the two ortho dinitrile groups separates the dinitrile groupsenough to permit polymerization. Presently several bridging groups areknown. Examples include aliphatic and unsaturated groups, aromaticgroups, aliphatic and aromatic diamide groups, and aliphatic andaromatic ether, sulfone and ketone groups.

The chemical and physical properties of the polymers depend primarily onthe bridging groups. The groups providing the best properties are thosewith aromatic, polar and flexible moieties, especially the --O--φ--φ--Ogroup of U.S. Pat. No. 4,259,471 by Keller et al., the --O--φ--C₃ F₆--φ--O-- of U.S. Pat. No. 4,238,601 by Keller et al., the --O--C₃ --H₆--φ--O-- group of U.S. Pat. No. 4,223,123 by Keller el. at, the--O--φ--SO₂ --φ--O-- and --O--φ--(C═O)--φ--O-- groups of U.S. Pat. No.4,234,712 by Keller el at and the --O--C_(n) --H_(2n) --O-- group ofU.S. Pat. No. 4,226,801 by Keller el al. These polymers have exceptionalthermal and oxidative stability, low water absorptivity, high strength,good dimensional integrity and strong adhesion. The aromatic moietiesprovide the high mechanical strength, modulus and high thermal andoxidative stability and the polar moieties provide the excellentadhesive properties.

U.S. Pat. No. 4,408,035 teaches curing of phthalonitrile monomers with anucleophilic aromatic amine. The monomer, 4,4'-bis(3,4-dicyanophenoxy)biphenyl, has a melting point of 232°-234° C.The aromatic diamines covered in the above patent are somewhat volatileat the required processing melt temperature, causing void problems whenused in an amount greater than 5% by weight. It is advantageous for aresin not to produce gaseous products when cured. Also, the chemicalmakeup of the polymer must be such that it consists of units havingknown resistance to bond-rupture under thermal, oxidative and hydrolyticconditions.

U.S. patent application Ser. No. 07/273,443 discloses1,3-bis(3-aminophenoxy)benzene and other bis(aminophenoxy) compoundsused as a curing agent for a rapid synthesis of phthalonitrile resin.The time and temperature needed for polymerization of bisphenol-linkedphthalonitrile monomers are easily controlled as a function of theconcentration of amine curing agent.

The necessity for aromatic and heterocyclic ring structure in a polymerto achieve heat resistance has long been recognized. The ideal heatresistant polymer would be composed of aromatic and/or heteroaromaticring structures interconnected by flexible linkages within the polymericbackbone to improve processability and to enhance the mechanicalproperties. However, few synthetic methods are available forincorporating stable linkages into a polymeric system.

SUMMARY OF THE INVENTION

Accordingly, an object of this invention is to synthesize phthalonitrilemonomers, polymers and copolymers with excellent thermal and oxidativeproperties and good mechanical properties in excess of 300° C.

And, an object of this invention is to produce polymeric materials forcomposite matrices to be used in applications where the use temperatureis above the operating temperature for conventional high temperaturepolymers and below the operating temperature for ceramics or metals.

Also, an object of this invention is to produce polymeric material whichare free of voids.

Further, an object of this invention is to provide new type ofphthalonitrile resins having aromatic imide and ether linkages in thebridge connecting the terminal phthalonitrile polymerizable units.

Additionally, an object of this invention is to provide a resin which ismore resistant to oxidative attack than epoxies, bismaleimides and otherconventional thermosetting polyimides.

These and other objects are accomplished by reacting anaminophenoxyphthalonitrile with an aromatic anhydride to produce an amicacid linked phthalonitrile which can be imidized either by chemicaland/or thermal means. The resulting phthalonitrile resin is processedeither alone or in the presence of a bisphenol-based phthalonitrilewhich behaves as a reactive plasticizer. Polymerization of the neatresin or polymeric blend is achieved by heating above the melting pointor softening temperature in the absence or presence of aromatic di- orpoly-amines, metal and/or metallic salts.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The imide-containing phthalonitrile monomers of this invention arerepresented by the formula: ##STR1## where R is an aromatic tetravalentradical or substituted aromatic tetravalent radical. By the word"substituted", it is meant in this application that any knownsubstituent could be attached to the aromatic moiety. Substituentsinclude but are not limited to halogens, chalcogens and organicradicals, such as phenyl, alcohol, carboxyl, carbonyl, or aliphaticgroups of less than 10 carbon atoms. The preferred compounds are where Ris an aromatic tetravalent radical of the general formula: ##STR2##where X is ##STR3## any alkyl of six carbons or fewer or any partiallyor perhalogenated alkyl of six carbons or fewer.

The most preferred compounds are where R is an aromatic tetravalentradical of the general formula: ##STR4## where X is ##STR5##

The imide-containing phthalonitrile monomers of this invention areprepared in solution by reaction of their precursors, 4-(3- or4-aminophenoxy) phthalonitrile and an aromatic anhydride. Thephthalonitrile monomers are synthesized by reaction of 4-(3- or4-aminophenoxy) phthalonitrile with an aromatic anhydride. Uponisolation by pouring the reaction mixture into an appropriateprecipitating solvent such as ethanol, complete imidization is achievedthermally in air at 300° C.

The imide-containing phthalonitrile monomers are prepared from 4-(3- or4-aminophenoxy)phthalonitrile and an aromatic anhydride according to thefollowing process: ##STR6## where R is as described above.

The 4-(3- or 4-aminophenoxy)phthalonitrile is prepared according to thefollowing process: ##STR7##

Examples of the preferred anhydrides which are suitable for use in thisinvention are listed below:

4,4'-(hexafluoroisopropylidene)diphthalic anhydride pyromelliticdianhydride

3,3',4,4'-benzophenonetetracarboxylic dianhydride

2,3,6,7-naphthalene tetracarboxylic dianhydride 3,3',4,4'-diphenyltetracarboxylic dianhydride

1,3,5,6-naphthalene tetracarboxylic dianhydride

2,2'3,3'-diphenyl tetracarboxylic dianhydride

2,2-bis(3,4-dicarboxyphenyl)propane dianhydride

bis(3,4-dicarboxyphenyl)ether dianhydride

naphthalene-1,2,4,5-tetracarboxylic dianhydride

naphthalene-1,4,5,8-tetracarboxylic dianhydride

decahydronaphthalene-1,4,5,8-tetracarboxylic dianhydride

4,8-dimethyl-1,2,3,5,6,7-hexahydronaphthalene-1,2,5,6-tetracarboxylicdianhydride

2,6-dichloronaphthalene-1,4,5,8-tetracarboxylic dianhydride

2,7-dichloronaphthalene-1,4,5,8-tetracarboxylic dianhydride

2,3,6,7-tetrachloronaphthalene-1,4,5,8-tetracarboxylic dianhydride

phenanthrene-1,8,9,10-tetracarboxylic dianhydride

2,2-bis(2,3-dicarboxyphenyl)propane dianhydride

1,1-bis(2,3-dicarboxyphenyl)ethane dianhydride

1,1-bis(3,4-dicarboxyphenyl)ethane dianhydride

bis(2,3-dicarboxyphenyl)methane dianhydride

bis(3,4-dicarboxyphenyl)methane dianhydride

bis(3,4-dicarboxyphenyl)sulfone dianhydride

benzene-1,2,3,4-tetracarboxylic dianhydride

4,4'-oxydiphthalic dianhydride

4,4'-thiophthalic dianhydride

The most preferred anhydrides are 3,3',4,4'-benzophenonetetracarboxylicdianhydride and 4,4'-(hexafluoroisopropylidene)diphthalic anhydride.

The imide-containing phthalonitrile polymers of this invention containthe repeating unit represented by the formula: ##STR8## where R is anaromatic tetravalent radical or substituted aromatic tetravalent radicalas defined above. The preferred compounds are where R is an aromatictetravalent radical of the general formula: ##STR9## where X is##STR10## any alkyl of six carbons or fewer or any partially orperhalogenated alkyl of six carbons or fewer.

The most preferred compounds are where R is an aromatic tetravalentradical of the general formula: ##STR11## where X is ##STR12##

Polymerization of the phthalonitrile monomer is accomplished by heatingthe monomer mixture above its melting point, continued heating at atemperature above the glass transition temperature of the prepolymeramorphous reactants until the mixture reaches its gelation point, curingthe mixture to complete crosslinking of the polymer and postcuring at atemperature from above the glass transition temperature of the polymerup to just below the carbonization temperature. Examples of cure cyclesfor neat polymerization are 1) a two-part cure of 225°-280° C. for 6-20hours and 300°-315° C. for 10-20 hours; 2) a three-part cure of225°-280° C. for 6-16 hours, 240°-300° C. for 2-6 hours and 300°-315° C.for 5-16 hours. The preferred two-part cure is 240° C. for 17 hours and315° C. for 16 hours. The preferred three-part cure is 225° C. for 16hours, 280° C. for 6 hours and 315° C. for 16 hours. The most preferredcure is the three-part cure.

The time and temperature needed for polymerization can be reduced bycuring phthalonitrile resins in the presence of amine curing agents thatare stable at the initially required processing temperatures. Theseamine curing agents do not volatilize during the polymerizationreaction. The amine curing agents are of the general formula YNH₂ whereY is an aromatic. The amount of curing agent added should be in therange of 1 to 10 weight percent of the polymer mixture. The preferredamount of curing agent is 1 to 5 weight percent. The most preferredamount of curing agent is 1.5 to 2.0 weight percent.

Specific examples of amine curing agents useful in this invention aregiven below:

o-phenylenediamine

m-phenylenediamine

p-phenylenediamine

4,4'-diaminodiphenylpropane

4,4'-diaminodiphenylmethane (commonly named 4,4'-methylenedianiline)

4,4'-diaminodiphenyl sulfide (commonly named 4,4'-thiodianiline)

4,4'-diaminodiphenyl ether (commonly named 4,4'-oxydianiline)

1,5-diaminonaphthalene

3,3'-dimethylbenzidine

3,3'-dimethoxybenzidine

2,4-bis(β-amino-t-butyl)toluene

bis(p-β-amino-t-butyl)ether

bis(p-β-methyl-o-aminopentyl)benzene

1,3-diamino-4-isopropylbenzene

1,2-bis(3-aminopropoxy)ethane

benzidine

m-xylylenediamine

p-xylylenediamine

2,4-diaminotoluene

2,6-diaminotoluene

1,3-bis(3-aminophenoxy)benzene

3-bis(4-aminophenoxy)benzene

1,4-bis(3-aminophenoxy)benzene

1,4-bis(4-aminophenoxy)benzene

bis[4-(3-aminophenoxy)phenyl]sulfone

bis[4-(4-aminophenoxy)phenyl]sulfone

4,4'-bis(3-aminophenoxy)biphenyl

4,4'-bis(4-aminophenoxy)biphenyl

2,2-bis[4-(3-aminophenoxy)phenyl]propane

2,2-bis[4-(4-aminophenoxy)phenyl]propane

The most preferred amine curing agent is 1,3-bis(3-aminophenoxy) benzene(APB).

Examples of cure cycles for polymerization with amine curing agentsare 1) a two-part cure of 225°-260° C. for 5-20 hours and 300°-315° C.for 5-20 hours; 2) a three-part cure of 180°-240° C. for 2-6 hours,240°-300° C. for 2-8 hours and 300°-315° C. for 10-20 hours; 3) afour-part cure of 180°-200° C. for 1-3 hours, 200°-240° C. for 2-4hours, 240°-280° C. for 4-6 hours and 300°-315° C. for 10-20 hours. Thepreferred two-part cure is 225° C. for 6 hours and 315° C. for 16 hours.The preferred three-part cure is 225° C. for 16 hours, 280° C. for 6hours and 315° C. for 16 hours. The preferred four-part cure is 200° C.for 2 hours, 240° C. for 3 hours, 280° C. for 5 hours and 315° C. for 16hours. The most preferred cure is the three-part cure.

After the cure cycle is complete, a postcure can be carried out toimprove the mechanical and thermal properties of the material. Thepreferred postcure is 325°-365° C. for 2-6 hours and 365°-385° C. for5-24 hours. The most preferred postcure is 350° C. for 4 hours and 375°C. for 12 hours. When postcure temperatures are in excess of 316° C.,heating is under an inert atmosphere, such as nitrogen or argon.

It should be noted that the cure cycles and postcures given above arenot intended to be complete and all inclusive. Other cure cycles andpostcures are possible depending on variations in time, temperature andadditives.

Polymerization and thus processibility phthalonitrile monomers aresomewhat difficult due to the enhanced viscosity of these monomerscompared to the bisphenol-based phthalonitrile of U.S. patentapplication Ser. No. 07/273,443. A reduction in the viscosity wasachieved by copolymerizing the imide-containing phthalonitrile withthese bisphenol-based phthalonitriles. The bisphenol-basedphthalonitriles behave as reactive plasticizer. As the term implies, therole of the reactive plasticizer is to improve the processability andthen, through reaction with the imide-containing phthalonitriles anditself, become a part of the cured resin system. Blends ofimide-containing phthalonitrile and bisphenol-based phthalonitrile canbe fabricated without seriously compromising the use properties. Theamount of bisphenol-based phthalonitrile is in the range from 10% to 50%by weight. The preferred amount is in the range from 20% to 30% byweight. The most preferred amount is approximately 25% by weight.

A general formula of the bisphenol-based phthalonitrile useful as areactive plasticizer is shown below: ##STR13## where A is any divalentorganic radical, for example, a bisphenol group, a diether group or adithioether group. The preferred diphthalonitrile monomers are those inwhich A in the formula above is a diether group, --R'--O. The mostpreferred diphthalonitrile monomers are those wherein R' is selectedfrom the class consisting of ##STR14## wherein φ is a phenyl group,wherein the phenyl groups are linked at tho para and the meta positionsand wherein "a" is any integer. The bisphenol-containing phthalonitrilemonomers copolymerize with the imide-containing phthalonitrile monomersto form a copolymer with the following repeating unit: ##STR15##

It is possible with the present invention to include a metal or metalsalt in the resins. For composite fabrication, a salt or a metal wouldbe less desirable because of problems with homogeneity and gassing.Examples of suitable metal salts include cuprous chloride, cuprousbromide, cuprous cyanide, cuprous ferricyanide, zinc chloride, zincbromide, zinc iodide, zinc cyanide, zinc ferrocyanide, zinc acetate,zinc sulfide, silver chloride, ferrous chloride, ferric chloride,ferrous ferricyanide, ferrous chloroplatinate, ferrous fluoride, ferroussulfate, cobaltous chloride, cobaltic sulfate, cobaltous cyanide, nickelchloride, nickel cyanide, nickel sulfate, nickel carbonate, stannicchloride, stannous chloride hydrate, a complex of triphenylphosphineoxide and stannous chloride (2TPPO/SnCl₂) and mixtures thereof. Themetals which can used include chromium, molybdenum, vanadium, beryllium,silver, mercury, aluminum, tin, lead, antimony, calcium, barium,manganese, magnesium, zinc, copper, iron, cobalt, nickel, palladium andplatinum. Mixtures of these metal may also be used. The preferred metalsare copper, silver and iron.

The invention having been generally described, the following examplesare given as particular embodiments of the invention and to demonstratethe practice and advantages thereof. It is understood that the examplesare given by way of illustration and are not intended to limit thespecification or the claims to follow in any manner.

EXAMPLE I Synthesis of Imide-Containing Phthalonitrile from3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA) and4-(3-aminophenoxy)phthalonitrile

To a 100ml three-necked flask was added3,3',4,4'-benzophenonetetracarboxylic dianhydride (5.4 g, 16.7 mmol) and30 ml of dry dimethylformamide (DMF). After flushing the solution withnitrogen for 20 minutes, 4-(3-aminophenoxy) phthalonitrile (7.8 g, 33.3mmol) was added under ambient conditions. The temperature of thereaction mixture was increased to 90° C. and held at this temperaturefor 1 hour. Toluene (30 ml) was added and the solution was heated toreflux. The water which was formed as a by-product was azeotroped fromthe mixture with a Dean Stark trap. Total reflux time was 12 hours.After removing the toluene by distillation and cooling, the whitesolidified product mixture was removed from the reaction vessel washedwith ethanol, collected by filtration, dried and annealed at 200° C. for2 hours to afford 11.9 g (93%) of imide-containing phthalonitrile, m.p.245°-248° C.

EXAMPLE II Synthesis of 6F Imide-Containing Phthalonitrile from4,4'-(hexafluoroisopropylidene)diphthalic Anhydride and4-(3-aminophenoxy)phthalonitrile

To a 100 ml three necked flask was added4,4'-hexafluoroisopropylidene)diphthalic anhydride (5.0 g, 11.3 mmol)and 30 ml of dry dimethylformamide (DMF). After thoroughly flushing thesolution with nitrogen, 4-(3-aminophenoxy) phthalonitrile (5.3 g, 22.3mmol) was added under ambient conditions. The temperature of thereaction mixture was increased to 90° C. and held at this temperaturefor 1 hour. Toluene (30 ml) was added and the solution was heated toreflux. Water as formed was azeotroped from the mixture with aDean-Stark trap. After refluxing for 12 hours, the toluene was removedby distillation. Upon cooling the product mixture was removed from thereaction vessel, washed several times with ethanol, collected by suctionfiltration, dried and annealed at 200° C. for 4 hours to complete theimidization reaction resulting in the formation of an amorphousmaterial.

EXAMPLE III Neat Polymerization of BTDA-Derived Imide Phthalonitrile

A 1 g sample of the imide-containing phthalonitrile was placed in analuminum planchet and degassed in a specially designed desiccator forevacuation purposes at 280° C. for 3 hours. The viscous monomer was thenplaced in a oven preheated to 280° C. and cured in air by heating at280° C. for 17 hours (overnight) and at 315° C. for 16 hours. Uponcooling the polymer was removed from the planchet and found to bevoid-free. A portion of the polymer was then postcured under anoxygen-free argon atmosphere at 350° C. for 4 hours and at 375° C. for12 hours. The thermal and oxidative properties were enhanced as a resultof the postcure treatment.

EXAMPLE IV Polymerization of BTDA-Derived Imide Phthalonitrile withAmine Additive

A 1.0 g sample of BTDA-imide-containing phthalonitrile was placed in analuminum planchet and degassed at 300° C. for 4 hours in a speciallydesigned desiccator for evacuation purposes. After cooling to 250° C.,1,3-bis(3-aminophenoxy)benzene (APB, 2% by weight) was added to theviscous sample with stirring. After 2 hours at 250° C., the sample hadgelled and become rubbery. The sample was then heated at 280° C. for 6hours and at 315° C. for 16 hours (overnight). Thermogravimetricanalysis (TGA) of powdered samples under both air and inert atmospheresshowed no decomposition before 350° C. Between 550°-650° C.,catastrophic oxidative degradation occurred. At 800° C. under a nitrogenatmosphere, the polymer exhibited a char yield of 60%.

EXAMPLE V Polymerization of BTDA-Derived Imide Phthalonitrile with AmineAdditive

A 0.5 g sample of BTDA-imide-containing phthalonitrile was placed in analuminum planchet and degassed at 300° C. for 3 hours as in Example III.At this time, the sample was cooled to 210° C. and APB (5 mmol, 1% byweight) was added with stirring to the viscous monomer. The sample wasthen placed in an oven and cured by heating at 200° C. for 2 hours, at220° C. for 3 hours and at 260° C. for 5 hours and at 315° C. for 16hours. The sample exhibited a glass transition temperature (T_(g)) of177° C. as determined by differential scanning calorimeter (DSC). Whenfurther postcured in a sequence under an oxygen-free argon atmosphere at350° C. for 4 hours and at 375° C. for 12 hours, the sample did notexhibit a T_(g).

EXAMPLE VI Polymerization of BTDA-Derived Imide Phthalonitrile withStannous Chloride

A 0.5 g sample of the BTDA-imide-containing phthalonitrile was placed inan aluminum planchet and degassed as in Example III. To the melt as 260°C. was added SnCl₂.H₂ O (0.035 g, 7% by weight) with stirring. Theviscosity started to increase rapidly. Full gelation had occurred within3 minutes. To complete the cure, the sample was heated at 260° C. for 6hours and a 300° C. for 16 hours. Upon cooling, the polymer was removedfrom the planchet and appeared tough.

To another sample of the monomer (0.5 g) was added SnCl₂.H₂ O (0.018 g,3.6% by weight) with stirring at 260° C. Solidification occurred within5 minutes at 260° C. To complete the cure the sample was heated at 260°C. for 6 hours and at 315° C. for 16 hours.

To a third sample of the monomer (0.5 g) was added SnCl₂.H₂ O (0.005 g,1% by weight) with stirring at 260° C. Full gelation was somewhatslower. Solidification had occurred after 20 minutes. To complete thecure, the sample was heated at 260° C. for 2 hours and at 315° C. for 16hours.

EXAMPLE VII Polymerization of 6F Imide-Containing Phthalonitrile withAmine Additive

A 0.5 g sample of the 6F imide-containing phthalonitrile was placed in aaluminum planchet and degassed as in Example III. To the melt was added0.01 g of APB (2% by weight) with stirring. The sample was cured byheating at 260° C. for 3 hours and at 300° C. for 5 hours and at 315° C.for 10 hours. The polymer showed excellent thermo-oxidative stability asdetermined by TGA with the initial weight loss commencing at about 450°C. and the catastrophic decomposition occurring between 500°-700° C. Inan inert atmosphere, the polymer exhibited a char yield of 60% at 800°C. When the polymer was postcured in sequence under an oxygen-free argonatmosphere at 350° C. for 4 hours and at 375° C. for 12 hour, it wasfound not to exhibit a T_(g). Moreover, an enhancement in thethermo-oxidative stability was observed with initial weigh losscommencing at temperature in excess of 500° C. No improvements in thethermal stability was observed.

EXAMPLE VIII Copolymer of BTDA-Derived Imide Phthalonitrile and4,4'-Bis(3,4-dicyanophenoxy)biphenyl Cured Neat

A sample containing 0.8 g of BTDA-imide-containing phthalonitrile and0.2 g of 4,4'-bis(3,4-dicyanophenoxy)biphenyl was thoroughly mixed in analuminum planchet and degassed in the melt at 260°-280° C. for 4 hoursat reduced pressure in a specially designed desiccator for evacuationpurposes. The monomeric blend, whose viscosity was considerably reducedrelative to the neat BTDA-imide-containing phthalonitrile itself, wascured by heating in air at 225° C. for 16 hours, at 280° C. for 6 hoursand at 315° C. for 16 hours. The blend solidified during the 225° C.heat treatment. The copolymer showed similar thermal and oxidativeproperties as found for the polymer derived solely from theBTDA-imide-containing phthalonitrile polymer. When the copolymer wasfurther post cured in sequence at 350° C. for 4 hours and at 375° C. for12 hours, it was found not to exhibit a T_(g).

EXAMPLE IX Copolymer of BTDA-Derived Imide Phthalonitrile and4,4'-Bis(3,4-dicyanophenoxy)biphenyl Cured with Amine Additive

A sample containing 0.8 g of BTDA-imide-containing phthalonitrile and0.2 g of 4,4'-bis(3,4-dicyanophenoxy)biphenyl was mixed in a aluminumplanchet and degassed as in Example VIII. To the melt of the blend wasadded 0.01 g of APB at 240° C. with stirring. The monomeric blend wasthen cured by heating in air at 225° C. for 16 hours (overnight), at280° C. for 8 hours and at 315° C. for 16 hours. Gelation occurredduring the 225° C. heat treatment.

EXAMPLE X Copolymer of BTDA-Derived Imide Phthalonitrile (70%) and4,4'bis(3,4-dicyanophenoxy)biphenyl (30% ) Cured with 2% By Weight ofAmine Additive

A sample containing 0.70 g of BTDA-imide-containing phthalonitrile and0.30 g of 4,4'-bis(3,4-dicyanophenoxy)biphenyl was mixed in a aluminumplanchet and degassed as in Example VIII. The fluidity of the mixturewas such that it was easy to process the sample above 200° C. To themelt at 225° C. was added 0.02 g (2% by weight) of APB with stirring.The monomeric blend was then cured in air by heating at 225° C. for 6hours, at 280° C. for 2 hours and at 315° C. for 16 hours. Gelationoccurred during the 225° C. heat treatment.

EXAMPLE XI Copolymer of BTDA-Derived Imide Phthalonitrile (70%) andBis[4-(3,4-dicyanophenoxy)phenyl]2,2-propane (30% ) Cured with 3% ByWeight of Amine Additive

A sample containing 0.70 g of BTDA-imide-containing phthalonitrile and0.30 g of bis[4-(3,4-dicyanophenoxy)phenyl]2,2-propane was mixed in analuminum planchet and degassed as in Example VIII. Due to the lowviscosity of the mixture in the melt relative to that of pureBTDA-imide-containing phthalonitrile monomer, the resulting mixture waseasily processed above 200° C. To the melt of the monomeric blend at225° C. was added 0.03 g of APB (3% by weight). The mixture was stirredfor 15 minutes. The mixture was then cured in air at 225° C. for 16hours and at 315 for 6 hours.

EXAMPLE XII Copolymer of BTDA-Derived imide Phthalonitrile (70%) andBis[4-(3,4-dicyanophenoxy)phenyl] Sulfone (30%) Cured With 2% By Weightof Amine Additive)

A sample containing 0.70 g of BTDA-imide-containing phthalonitrile and0.30 g of bis[4-(3,4-dicyanophenoxy) phenyl]sulfone was placed in analuminum planchet and degassed as in Example VIII. To the melt of themonomeric blend was added 0.02 g of methylenedianiline (MDA) withstirring. The mixture was cured by heating in air at 225° C. for 4hours, at 280° C. for 4 hours and at 315° C. for 10 hours. Gelationoccurred during the heat treatment at 225° C.

EXAMPLE XIII Copolymer of BTDA-Derived imide Phthalonitrile (50%) andBis[4-(3,4-dicyanophenoxy)phenyl] Sulfone (50%) Cured With 2% By Weightof Amine Additive)

A sample containing 0.50 g of BTDA-imide-containing phthalonitrile and0.50 g of bis[4-(3,4-dicyanophenoxy) phenyl)sulfone was placed in analuminum planchet and degassed as in Example VIII. To the low viscositymelt at 200° C. was added 0.02 g of 1,3-bis(4-aminophenoxy)benzene withstirring. Soon after the addition of the amine compound, the temperatureof the mixture was reduced to 160° C. resulting in the reaction blendbecoming somewhat viscous. After stirring the monomeric blend at 160° C.for 30 minutes, it was placed in an oven preheated to 200° C. Gelationhad occurred after 2 hours at 200° C. To complete the cure, the samplewas further heated in air at 260° C. for 8 hours and at 300° C. for 16hours.

EXAMPLE XIV Copolymer of 6F Imide-Containing Phthalonitrile (70%) andBis[4-(3,4-dicyanophenoxy)phenyl]2,2-hexafluoropropane (30%) Cured Neat

A sample containing 0.70 g of 6F imide-containing phthalonitrile and0.30 g of bis[4-(3,4 dicyanophenoxy)phenyl]2,2-hexafluoropropane wasplaced in an aluminum planchet and degassed as in Example VIII. Theresulting monomeric blend was cured by heating in air at 240° C. for 16hours (overnight), at 280° C. for 2 hours, and at 315° C. for 6 hours.Gelation occurred during the 240° C. heat treatment.

EXAMPLE XV Copolymer of 6F Imide-Containing Phthalonitrile (60%) andBis[4-(3,4-dicyanophenoxy)phenyl]2,2-Hexafluoropropane (40%) with 1.5%By Weight of Amine Additive

A sample containing 0.50 g of 6F imide-containing phthalonitrile and0.40 g of bis[4-(3,4-dicyanophenoxy)phenyl]2,2-hexafluoropropane wasplaced in an aluminum planchet and degassed as in Example VIII. To themelt of the monomeric blend at 200° C. was added 0.15 g of APB withstirring. After stirring for 10 minutes at 200° C. , the sample wasplaced in an oven and cured by heating in air at 180° C. for 4 hours, at240° C. for 4 hours and at 300° C. for 20 hours.

The new phenoxy- and imide-containing polymers exhibit outstandingthermo-oxidative stability and have potential usage for aerospacecomposite applications in the 300°-375° C. range. Such material couldbridge the gap between currently used high temperature polymers andceramics and metal.

During polymerization of the new phthalonitrile resins containing etherand imide linkages, no volatiles are formed, resulting in void-freecomponents. The new resins exhibit better thermo-oxidative propertiesthan current commercially available high temperature materials, such asPMR-15 and Thermid 600. The mechanical properties of the new resinsshould be improved due to a reduction in the crosslinking density.

Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

What is claimed as new and desired to be secured by Letter of Patent ofthe United States is:
 1. A method of polymerization comprising:heating amonomer mixture above the mixture melting point to produce an amorphousprepolymer reactant mixture; heating the prepolymer mixture above theglass transition temperature thereof to produce a gelled polymermixture; curing the polymer mixture to crosslink the polymer;wherein themonomer mixture comprises monomers of the formula: ##STR16## where R isan aromatic tetravalent radical or substituted aromatic tetravalentradical.
 2. A method of polymerization as recited in claim 1 wherein thecuring is chosen from the group consisting of a two-part cure of225°-280° C. for 6-20 hours and 300°-315° C. for 10-20 hours and athree-part cure of 225°-280° C. for 6-16 hours, 240°-300° C. for 2-6hours and 300°-315° C. for 5-16 hours.
 3. A method of polymerization asrecited in claim 2 wherein the curing is at 225°-280° C. for 6-16 hours,240°-300° C. for 2-6 hours and 300°-315° C. for 5-16 hours.
 4. A methodof polymerization as recited in claim 3 wherein the curing is at 225° C.for 16 hours, 280° C. for 6 hours and 315° C. for 16 hours.
 5. A methodof polymerization as recited in claim 1 additionallycomprising:postcuring at a temperature from above the glass transitiontemperature of the polymer up to just below the carbonizationtemperature.
 6. A method of polymerization as recited in claim 5 whereinthe postcuring is at 325°-365° C. for 2-6 hours and 365°-385° C. for5-24 hours.
 7. A method of polymerization as recited in claim 5 whereinthe postcuring is at 350° C. for 4 hours and 375° C. for 12 hours.
 8. Amethod of polymerization as recited in claim 1 additionallycomprising:adding phthalonitrile monomers of the formula: ##STR17##where A is any divalent organic radical.
 9. A method of polymerizationas recited in claim 8 wherein A is a diether group.
 10. A method ofpolymerization as recited in claim 8 wherein A is a selected from theclass consisting of ##STR18## wherein φ is a phenyl group, wherein thephenyl groups are linked at the para and the meta positions and wherein"a" is an integer of at least one.
 11. A method of polymerization asrecited in claim 8 wherein the amount of phthalonitrile is in the rangefrom 10% to 50% by weight.
 12. A method of polymerization as recited inclaim 8 wherein the amount of phthalonitrile is in the range from 20% to30% by weight.
 13. A method of polymerization as recited in claim 8wherein the amount of phthalonitrile is approximately 25% by weight. 14.A polymer produced according to the process of claim 1 and comprisingrepeating units of the formula: ##STR19##
 15. A polymer having therepeating unit of the general formula: ##STR20## where R is an aromatictetravalent radical or substituted aromatic tetravalent radical.
 16. Apolymer as recited in claim 1 wherein R is an aromatic tetravalentradical or substituted aromatic tetravalent radical of the generalformula: ##STR21## where X is ##STR22## any alkyl of six carbons orfewer or any partially or perhalogenated alkyl of six carbons or fewer.17. A polymer as recited in claim 16 wherein R is an aromatictetravalent radical or substituted aromatic tetravalent radical of thegeneral formula: ##STR23## where X is ##STR24##
 18. A copolymer producedaccording to the process of claim 8 and comprising:repeating units ofthe general formula: ##STR25## and repeating units of phthalonitrile ofthe general formula: ##STR26## wherein A and R are as defined above. 19.A copolymer as recited in claim 18 wherein A is a diether group.
 20. Acopolymer as recited in claim 19 wherein A is a selected from the classconsisting of ##STR27## wherein φ is a phenyl group, wherein the phenylgroups are linked at the para and the meta positions and wherein "a" isan integer of at least one.
 21. A copolymer as recited in claim 18wherein the amount of bisphenol-based phthalonitrile is in the rangefrom 10% to 50% by weight.
 22. A copolymer as recited in claim 20wherein the amount of bisphenol-based phthalonitrile is in the rangefrom 20% to 30% by weight.
 23. A copolymer as recited in claim 21wherein the amount of bisphenol-based phthalonitrile is approximately25% by weight.